During cardiac surgery, circulation of blood through a patient's body may be maintained by connecting the patient to an extracorporeal system, such as a heart-lung machine. The heart-lung machine adds oxygen to and removes carbon dioxide from the blood, heats or cools the blood, and provides impetus to the blood to cause the blood to circulate through the patient's vascular system.
Connecting a patient to a extracorporeal system is typically done by inserting a cannula into the patient's venous system near or in the heart to remove blood from the patient and direct it to the extracorporeal circuit. After the blood has passed through the extracorporeal circuit, the blood is infused into the patient's arterial system near the heart.
The venous cannula that is inserted into the heart to siphon blood away for entry into the heart-lung machine is typically inserted into the right atrium and/or vena cava. The venous cannula may be a single stage device having one set of input apertures or a two-stage device used to simultaneously drain the right atrium and superior vena cava through an atrial basket while the inferior vena cava is drained through another set of apertures at the distal tip of the cannula. Oxygenated blood is returned to the heart from the heart-lung machine using an arterial cannula to return blood to the aorta.
In order to maintain proper blood flow rate through a cannula, the cannula body typically has a wire support, such as a helical reinforcement spring to prevent kinking or other degradation of the lumen extending through the cannula body. Additionally, it is often desired to have a malleable cannula that may be bent into a particular configuration and that maintains the chosen configuration during use. Such malleability may be provided by the inclusion of a malleable member, such as a relatively stiff wire extending along the length of the cannula body, the malleable member maintaining the cannula in a particular shape chosen by the surgeon.
The construction of a suitable malleable cannula presents certain design challenges. The addition of a malleable member may compromise the cross-sectional area of the lumen, thus degrading the flow rate provided by a particular size cannula. For example, a cannula having a particular outside diameter may have a 25–35 percent reduction in flow through the lumen when a malleable member is added to the design. Accordingly, to achieve the same flow rate, a cannula having a larger outside diameter may need to be chosen, which may not be desirable given the larger aperture necessary for insertion of the larger cannula into a particular portion of the heart.
Another design issue that arises with respect to the addition of a malleable member to a cannula is the issue of how to anchor the malleable member within the cannula body. Although a cannula is typically molded of a plastic material that will help to keep a malleable wire in place, when the cannula body is bent and twisted in a variety of directions by the surgeon during use, the wire may shift in the cannula body due to the changing curvature of the outer wall of the cannula. Further, movement of the malleable wire with respect to the cannula wall may result in damage to the cannula wall by the wire and the possible puncture of the cannula wall by the wire under certain circumstances.
There is a need for a cannula that is malleable but does not have a reduction in the flow rate for a given size cannula. Further, there is a need for a method and apparatus for improved anchoring of a malleable member within a cannula body. Further, there is a need for malleable member that is configured to not permit damage to the cannula wall by movement of the malleable member when the cannula is shaped during use.
It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed herein extend to those embodiments that fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs.